1. Field of the Invention
The present invention relates to an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject.
2. Related Art Statement
A blood pressure of an inferior limb (hereinafter, referred to as xe2x80x9cinferior-limb blood pressurexe2x80x9d) of a normal person is higher than a blood pressure of a superior limb (hereinafter, referred to as xe2x80x9csuperior-limb blood pressurexe2x80x9d) of the person. However, if arteries of the inferior limb of the person suffer stenosis, the inferior-limb blood pressure may be lower than the superior-limb blood pressure. This can be utilized to diagnose the stenosis of arteries of inferior limb. For example, European Patent Document No. 1053714 A2 discloses a superior-and-inferior-limb blood-pressure index measuring apparatus which determines a superior-and-inferior-limb blood-pressure index as a ratio of an inferior-limb blood pressure to a superior-limb blood pressure or a ratio of a superior-limb blood pressure to an inferior-limb blood pressure.
The determination of superior-and-inferior-limb blood-pressure index needs measurements of inferior-limb blood pressure and superior-limb blood pressure. To this end, generally, those blood-pressure measuring devices are used which include respective inflatable cuffs adapted to be wound around an inferior limb and a superior limb of a living subject and each of which determines a blood pressure based on a signal occurring to a corresponding one of the cuffs when a pressure in the cuff is slowly changed. The blood-pressure measuring devices utilizing the cuffs provide highly reliable blood-pressure values. Since a superior-and-inferior-limb blood-pressure index determined based on inferior-limb and superior-limb blood-pressure values measured using cuffs is highly reliable, the diagnosis of stenosis of arteries of inferior limb can be made with accuracy.
However, when a blood-pressure measuring device utilizing an inflatable cuff is used to measure a blood pressure of a patient, it is needed to increase a pressure in the cuff up to a prescribed target pressure higher than a systolic blood pressure of the patient. In addition, since an inferior-limb blood pressure of a normal person is higher than a superior-limb blood pressure of the person, it is needed, when the inferior-limb blood pressure is measured, to increase the pressure of the cuff up to a higher target pressure than the target pressure employed for the measurement of superior-limb blood pressure. For example, a target pressure employed by a superior-limb-blood-pressure measuring device is about 180 mmHg, whereas a target pressure employed by an inferior-limb-blood-pressure measuring device is about 240 mmHg. Thus, when an inferior-limb blood pressure is measured from a patient, the patient feels more discomfort than when a superior-limb blood pressure is measured from the same.
It is therefore an object of the present invention to provide a superior-and-inferior-limb blood-pressure index measuring apparatus which allows diagnosis of stenosis of inferior-limb artery of a patient, without causing the patient to feel much discomfort.
The Inventor has carried out extensive studies and found that information obtained from an inferior-limb pulse wave contains information (hereinafter, referred to as xe2x80x9cstenosis-relating pulse-wave informationxe2x80x9d) that changes in relation with a degree of stenosis of inferior-limb artery. If a superior-and-inferior-limb blood-pressure index is measured only when a preliminary judgment made about the stenosis of inferior-limb artery based on the stenosis-relating pulse-wave information indicates that the inferior-limb artery is suspected of the stenosis, diagnosis of stenosis of inferior-limb artery of a patient can be made without causing the patient to feel much discomfort. The present invention has been developed based on this finding.
The above object has been achieved by the present invention. According to the present invention, there is provided an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject, comprising an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject, comprising an inferior-limb-blood-pressure measuring device which includes at least one inferior-limb cuff adapted to be wound around at least one inferior limb of the subject and which measures at least one inferior-limb blood pressure of the inferior limb; a superior-limb-blood-pressure measuring device which includes at least one superior-limb cuff adapted to be wound around at least one superior limb of the subject and which measures at least one superior-limb blood pressure of the superior limb; a blood-pressure-index determining means for determining the superior-and-inferior-limb blood-pressure index, based on the inferior-limb blood pressure measured by the inferior-limb-blood-pressure measuring device and the superior-limb blood pressure measured by the superior-limb-blood-pressure measuring device; an inferior-limb-pulse-wave detecting device which is adapted to be worn on an inferior limb of the subject and which detects an inferior-limb pulse wave from the inferior limb; and a stenosis-relating-pulse-wave-information obtaining device which obtains, based on the inferior-limb pulse wave detected by the inferior-limb-pulse-wave detecting device, stenosis-relating pulse-wave information which changes in relation with a degree of stenosis of an artery of the inferior limb.
According to this invention, before the inferior-limb-blood-pressure measuring device measures the inferior-limb blood pressure, the stenosis-relating-pulse-wave-information obtaining device may obtain, from the inferior-limb pulse wave detected by the inferior-limb-pulse-wave detecting device, the stenosis-relating pulse-wave information. If the thus obtained stenosis-relating pulse-wave information indicates that the artery of the inferior limb is not suspected of the stenosis, the inferior-limb-blood-pressure measuring device need not measure the inferior-limb blood pressure to determine the superior-and-inferior-limb blood-pressure index. Therefore, the diagnosis of stenosis of inferior-limb artery can be made without causing the subject to feel much discomfort. This diagnosis may be made either automatically by the apparatus, or by a living person.
Preferably, the apparatus further comprises a preliminary-judgment making means for making a preliminary judgment that the artery of the inferior limb is suspected of the stenosis, when the stenosis-relating pulse-wave information obtained by the stenosis-relating-pulse-wave-information obtaining device falls in a predetermined abnormal range; and a blood-pressure-measurement starting means for, when the preliminary-judgment making means makes the preliminary judgment that the artery of the inferior limb is suspected of the stenosis, starting the inferior-limb-blood-pressure measuring device to measure the inferior-limb blood pressure of the inferior limb, and starting the superior-limb-blood-pressure measuring device to measure the superior-limb blood pressure of the superior limb, so that the blood-pressure-index determining means determines the superior-and-inferior-limb blood-pressure index, based on the inferior-limb blood pressure measured by the inferior-limb-blood-pressure measuring device and the superior-limb blood pressure measured by the superior-limb-blood-pressure measuring device.
According to this feature, when the preliminary-judgment making means makes the preliminary judgment that the artery of the inferior limb is suspected of the stenosis, the blood-pressure-measurement starting means automatically starts the inferior-limb-blood-pressure measuring device to measure the inferior-limb blood pressure of the inferior limb, and starts the superior-limb-blood-pressure measuring device to measure the superior-limb blood pressure of the superior limb, and finally the blood-pressure-index determining means automatically determines the superior-and-inferior-limb blood-pressure index, based on the thus measured inferior-limb blood pressure and the thus measured superior-limb blood pressure.
Preferably, the stenosis-relating-pulse-wave-information obtaining device comprises at least one of (a) an inferior-limb-pulse-wave-propagation-velocity-relating-information obtaining device which obtains, based on the inferior-limb pulse wave detected by the inferior-limb-pulse-wave detecting device, inferior-limb -pulse-wave-propagation-velocity-relating information relating to a velocity at which the inferior-limb pulse wave propagates through the artery of the inferior limb, (b) a sharpness-degree determining means for determining a degree of sharpness of a heartbeat-synchronous pulse of the inferior-limb pulse wave detected by the inferior-limb-pulse-wave detecting device; and (c) an increase-characteristic-value determining means for determining a characteristic value of an increasing portion of a heartbeat-synchronous pulse of the inferior-limb pulse wave detected by the inferior-limb-pulse-wave detecting device.
Preferably, the stenosis-relating-pulse-wave-information obtaining device comprises an inferior-limb-pulse-wave-propagation-velocity-relating-information obtaining device which obtains, based on the inferior-limb pulse wave detected by the inferior-limb-pulse-wave detecting device, inferior-limb-pulse-wave-propagation-velocity-relating information relating to a velocity at which the inferior-limb pulse wave propagates through the artery of the inferior limb, and the apparatus further comprises a superior-limb-pulse-wave detecting device which is adapted to be worn on a superior limb of the subject and which detects a superior-limb pulse wave from the superior limb; a superior-limb-pulse-wave-propagation-velocity-relating-information obtaining device which obtains, based on the superior-limb pulse wave detected by the superior-limb-pulse-wave detecting device, superior-limb-pulse-wave-propagation-velocity-relating information relating to a velocity at which the superior-limb pulse wave propagates through an artery of the superior limb; a normal-range determining means for determining, based on the superior-limb-pulse-wave-propagation-velocity-relating information obtained by the superior-limb -pulse-wave-propagation-velocity-relating-information obtaining device, a normal range of inferior-limb-pulse-wave-propagation-velocity-relating information, according to a predetermined relationship between inferior-limb-pulse-wave-propagation-velocity-relating information and superior-limb-pulse-wave-propagation-velocity-relating information; and a preliminary-judgment making means for making a preliminary judgment that the artery of the inferior limb is suspected of the stenosis, when the inferior-limb-pulse-wave-propagation-velocity-relating information obtained by the inferior-limb-pulse-wave-propagation-velocity-relating-information obtaining device does not fall in the normal range determined by the normal range determining means.
According to this feature, the normal-range determining means determines, based on the superior-limb-pulse-wave-propagation-velocity-relating information, the normal range of inferior-limb-pulse-wave-propagation-velocity-relating information, according to the predetermined relationship, and the preliminary-judgment making means makes the preliminary judgment that the artery of the inferior limb is suspected of the stenosis, when the inferior-limb-pulse-wave-propagation-velocity-relating information obtained by the inferior-limb-pulse-wave-propagation-velocity-relating-information obtaining device does not fall in the thus determined normal range. Since the normal range is determined based on the superior-limb-pulse-wave-propagation-velocity-relating information actually obtained in each measuring operation, the preliminary judgment made about whether the inferior-limb artery is suspected of the stenosis is more accurate than a judgment which would be made in the case where inferior-limb-pulse-wave-propagation-velocity-relating information actually obtained is compared with a general-purpose normal range which is so pre-determined as to be applicable to a great number of patients.
Preferably, the inferior-limb-pulse-wave detecting device comprises two detecting members which are adapted to be worn on a left and a right inferior limb of the subject, respectively, and which detect a left-inferior-limb pulse wave and a right-inferior-limb pulse wave from the left and right inferior limbs, respectively, and the stenosis-relating-pulse-wave-information obtaining device comprises means for obtaining, based on the detected left-inferior-limb pulse wave, left-inferior-limb-stenosis-relating pulse-wave information which changes in relation with a degree of stenosis of an artery of the left inferior limb, and means for obtaining, based on the detected right-inferior-limb pulse wave, right-inferior-limb-stenosis-relating pulse-wave information which changes in relation with a degree of stenosis of an artery of the right inferior limb.
According to this feature, if the left-inferior-limb-stenosis-relating pulse-wave information obtained based on the left-inferior-limb pulse wave is compared with the right-inferior-limb-stenosis-relating pulse-wave information obtained based on the right-inferior-limb pulse wave and it is found that a difference between the two sorts of information is significantly great, it is said that there is possibility that the great difference would result from the stenosis of artery of at least one of the left and right inferior limbs. Thus, an accurate preliminary judgment about whether the arteries of inferior limbs are suspected of stenosis can be obtained.
Preferably, the apparatus further comprises a preliminary-judgment making means for making a preliminary judgment that the artery of at least one of the left and right inferior limbs is suspected of the stenosis, when a relative value between the obtained left-inferior-limb-stenosis-relating pulse-wave information and the obtained right-inferior-limb-stenosis-relating pulse-wave information is greater than a prescribed reference value.
According to this feature, if the relative value between the left-inferior-limb-stenosis-relating pulse-wave information and the right-inferior-limb-stenosis-relating pulse-wave information is greater than the prescribed reference value, the preliminary-judgment making means makes the preliminary judgment that the artery of at least one of the left and right inferior limbs is suspected of the stenosis. Thus, an accurate preliminary judgment about whether the artery of the inferior limb is suspected of stenosis can be made.